1. Field of the Invention
This invention relates to an automatic control type electronic flash unit for flash photography which is capable of automatically controlling the quantity of its emitted light, and more particularly, to a device for indicating whether the quantity of light emitted by the flash unit is proper.
2. Description of the Prior Art
In automatic control type electronic flash units the quantity of the flashlight reflected by an object to be photographed is measured by a metering circuit, and when such quantity of light has become sufficient to provide a proper exposure, the light emission of the flash lamp is discontinued by the output of the metering circuit. It has heretofore been proposed to cause an indicator device to be operated by the output of the above-mentioned metering circuit to indicate the emission of the quantity of flashlight sufficient for a proper exposure. However, a predetermined time delay exists from the generation of the output of the metering circuit until the actual discontinuation of the flashlight, and therefore, the flash lamp emits a predetermined quantity of excess flashlight during the predetermined time delay. Where the object to be photographed is distant from the camera and accordingly, a long flash time is necessary to provide a proper exposure, that is, where generation of a great quantity of flashlight is required, the aforementioned time delay is negligible as compared with that necessary long flash time, or to put it another way, the aforementioned quantity of excess light is negligible as compared with the necessary relatively great quantity of flashlight. However, where the object to be photographed lies near the camera so that a very short time of flash is required to provide a proper exposure, the aforementioned time delay is not negligible with respect to such short flash time and over-exposure will result from the abovementioned quantity of excess flashlight.